1. Field of the Invention
The invention generally relates to eFuses and more particularly to a silicided single crystal silicon eFuse.
2. Description of the Related Art
The below-referenced U.S. patents disclose embodiments that were satisfactory for the purposes for which they were intended. The disclosures of the below-referenced U.S. patents and Publications (sometimes referred to herein as “conventional references”), in their entireties, are hereby expressly incorporated by reference into the present invention for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art. U.S. Publications 2003/01344556, and 2002/0033519; and U.S. Pat. Nos. 6,633,055, 6,432,760, and 6,368,902 discloses conventional eFuses that utilize silicided polysilicon.
As discussed in the conventional references, computers typically have various types of devices which store data, such as memory devices. One type of memory device is a read only memory (ROM) device in which data is permanently stored and cannot be overwritten or otherwise altered. Thus, ROM devices are useful whenever unalterable data or instructions are required. ROM devices are also non-volatile devices, meaning that the data is not destroyed when power is shut off. ROM devices are typically programmed during fabrication by making permanent electrical connections in selected portions of the memory device. One disadvantage of ROM devices is that their programming is permanently determined during fabrication and, therefore, can only be changed by redesign.
Another type of memory device is a programmable read only memory (PROM) device. Unlike ROM devices, PROM devices are programmable after their design and fabrication. To render them programmable, PROM devices are typically provided with an electrical connection in the form of a fusible link (fuse). There are a considerable number of fuse designs used in PROM devices. Perhaps the most common fuse design is a metal or polysilicon layer which is narrowed or “necked down” in one region. To blow the fuse, a relatively high electrical current is driven though the metal or polysilicon layer. The current heats the metal or polysilicon above its melting point, thereby breaking the conductive link and making the metal layer or polysilicon discontinuous, or high resistance. Typically, the conductive link breaks in the narrowed region because the current density (and temperature) is highest in that region. The PROM device is thus programmed to conducting and non-conducting patterns, thereby forming the 1 or 0 comprising the data stored in the memory device.
Rather than employing an electrical current, a laser can be employed to blow the fuses. Using lasers instead of electrical current to blow fuses, however, has become more difficult as the size of memory devices decreases. As memory devices decrease in size and the degree of integration increases, the critical dimensions (e.g., fuse pitch) of memory cells become smaller. The availability of lasers suitable to blow the fuse becomes limited since the diameter of the laser beam should not be smaller than the fuse pitch. Thus, the fuse pitch, and the size of memory devices, becomes dictated by minimum diameter of laser beams obtainable by current laser technology.
The ability of electrical currents to blow fuses could aid in adapting fuses for a variety of applications, such as redundancy technology. Redundancy technology improves the fabrication yield of high-density memory devices, such as SRAM and DRAM devices, by replacing failed memory cells with spare ones using redundant circuitry which is activated by blowing fuses. Using laser beams to blow the fuses limits the size. Using electrical currents instead to blow fuses, therefore, has a greater potential for high-degree integration and decreased size of memory devices.